Systems and methods for controlling vapor phase processing

ABSTRACT

A semiconductor processing device can include a reactor assembly comprising a reaction chamber sized to receive a substrate therein. An exhaust line can be in fluid communication with the reaction chamber, the exhaust line configured to transfer gas out of the reaction chamber. A valve can be disposed along the exhaust line to regulate the flow of the gas along the exhaust line. A control system can be configured to operate in an open loop control mode to control the operation of the valve.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Field

The field relates to systems and methods for controlling vapor phaseprocesses, and in particular to systems and methods for controllingvapor phase processes in which overall flow rates vary duringprocessing.

Description of the Related Art

Atomic Layer Deposition (ALD) is a method for growing highly uniformthin films onto a substrate. In a time-divided ALD reactor, thesubstrate is placed into reaction space free of impurities and at leasttwo different volatile precursors (reactant vapors) are injected invapor phase alternately and repetitively into the reaction space. Thefilm growth is based on self-limiting surface reactions that take placeon the surface of the substrate to form a solid-state layer of atoms ormolecules, because the reactants and the temperature of the substrateare chosen such that the alternately-injected vapor-phase precursor'smolecules react only on the substrate with its surface layer. Thereactants are injected in sufficiently high doses for the surface to bepractically saturated during each injection cycle. Therefore, theprocess is highly self-regulating, being not very dependent on theconcentration of the starting materials, temperature or duration ofexposure (at least within relatively wide process windows) whereby it ispossible to achieve extremely high film uniformity and a thicknessaccuracy of a single atomic or molecular layer. Similar results can beobtained in space-divided ALD reactors, where the substrate is movedinto zones for alternate exposure to different reactants. Reactants cancontribute to the growing film (precursors) and/or serve otherfunctions, such as stripping ligands from an adsorbed species of aprecursor to facilitate reaction or adsorption of subsequent reactants.

The ALD method can be used for growing both elemental and compound thinfilms. ALD can involve alternate two or more reactants repeated incycles, and different cycles can have different numbers of reactants.Pure ALD reactions tend to produce less than a monolayer per cycle,although variants of ALD may deposit more than a monolayer per cycle.

Growing a film using the ALD method can be a slow process due to itsstep-wise (layer-by-layer) nature. At least two gas pulses arealternated to form one layer of the desired material, and the pulses arekept separated from each other for preventing uncontrolled growth of thefilm and contamination of the ALD reactor. After each pulse, the gaseousreaction products of the thin-film growth process as well as the excessreactants in vapor phase are removed from the reaction space, or thesubstrate is removed from the zone that contains them. In time-dividedexamples, this can be achieved by pumping down the reaction space, bypurging the reaction space with an inactive gas flow between successivepulses, or both. Purging employs a column of an inactive gas in theconduits between the reactant pulses. Purging is widely employed onproduction scale because of its efficiency and its capability of formingan effective diffusion barrier between the successive pulses. Regularly,the inert purging gas is also used as a carrier gas during reactantpulses, diluting the reactant vapor before it is fed into the reactionspace.

It can be challenging to control the transition from purging to dosing,and vice versa, while ensuring both high film quality and efficiency forin time and consumption of reactants. Accordingly, there remains acontinuing need for improved systems and methods for controllingdeposition processes.

SUMMARY

The systems and methods of the present disclosure have several features,no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, various features will now be discussedbriefly. After considering this discussion, and particularly afterreading the section entitled “Detailed Description,” one will understandhow the features described herein provide several advantages overtraditional gas delivery methods and systems.

In one embodiment, an atomic layer deposition (ALD) device is disclosed.The ALD device can comprise a reactor assembly comprising a reactionchamber sized to receive a substrate therein. The ALD device cancomprise an exhaust line in fluid communication with the reactionchamber, the exhaust line configured to transfer gas out of the reactionchamber. The ALD device can comprise a valve disposed along the exhaustline to regulate the flow of the gas along the exhaust line, the valvehaving a plurality of flow conductance settings. The ALD device cancomprise a control system configured to control the operation of thevalve. During a dose state of the ALD device, the control system can beconfigured to send a first signal to the valve corresponding to a firstflow conductance of the plurality of flow conductance settings. During apurge state of the ALD device, the control system can be configured tosend a second signal to the valve corresponding to a second flowconductance of the plurality of flow conductance settings.

In another embodiment, a semiconductor processing device is disclosed.The semiconductor processing device can comprise a reactor assemblycomprising a reaction chamber sized to receive a substrate therein. Thesemiconductor processing device can comprise an exhaust line in fluidcommunication with the reaction chamber, the exhaust line configured totransfer gas out of the reaction chamber. The semiconductor processingdevice can comprise a valve disposed along the exhaust line to regulatethe flow of the gas along the exhaust line. The semiconductor processingdevice can comprise a control system configured to operate in an openloop control mode to control the operation of the valve.

In another embodiment, a method of controlling an atomic layerdeposition (ALD) device is disclosed. The ALD device can comprise areaction chamber, an exhaust line that transfers gas out of the reactionchamber, and a valve along the exhaust line. The method can comprise,for a dose state of the ALD device, determining a first flow conductancesetting of the valve corresponding to a first flow conductance based atleast in part on a first desired pressure in the reaction chamber and afirst gas load for the dose state. The method can comprise, for a purgestate of the ALD device, determining a second flow conductance settingof the valve corresponding to a second flow conductance based at leastin part on a second desired pressure in the reaction chamber and asecond gas load for the purge state. The method can comprise placing thevalve at the first flow conductance setting for at least a portion ofthe dose state. The method can comprise pulsing a first reactant vaporinto the reaction chamber during the dose state. The method can compriseplacing the valve at the second flow conductance setting for at least aportion of the purge state. The method can comprise purging the reactionchamber by supplying an inactive gas to the reaction chamber during thepurge state.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will now be described with reference to the drawings ofseveral embodiments, which embodiments are intended to illustrate andnot to limit the invention.

FIG. 1A is a schematic side sectional view of a semiconductor processingdevice comprising a reactor assembly, shown during a processing stage.

FIG. 1B is a schematic side sectional view of the semiconductorprocessing device of FIG. 1A, shown during a load/unload stage.

FIG. 2 is a table of representative values of gas load (flow rate),valve control pressure, valve set point or position, measured pressurein the reaction chamber, and the difference between measured waferpressure and control pressure for the semiconductor processing deviceshown in FIGS. 1A-1B.

FIG. 3 is an example of a graph that plots measured reaction chamberpressures versus set points of a valve along an exhaust line of thesemiconductor processing device, plotted across a plurality of gasloads.

FIG. 4 is a schematic system diagram of a control system in electricalcommunication with the valve.

FIG. 5 is a flowchart illustrating a method for operating an ALD device,according to various embodiments.

FIG. 6A is a schematic plan view of a valve in a fully openconfiguration, according to various embodiments disclosed herein.

FIG. 6B is a schematic plan view of the valve of FIG. 6A in a fullyclosed configuration.

FIG. 7 is a graph of relative flow conductance over time for a purgecycle, followed by a dose cycle, followed by another purge cycle, usingthe valve shown in FIGS. 6A-6B.

DETAILED DESCRIPTION

Various embodiments disclosed herein relate to systems and methods forcontrolling a deposition process in a semiconductor processing device.While embodiments are described in the context of deposition devices(e.g., an atomic layer deposition (ALD) device, a chemical vapordeposition (CVD) device, etc.), the skilled artisan will appreciateapplication for the principles and advantages taught herein for othertypes of processing in which overall flow rates and/or pressure maychange frequently during processing.

FIG. 1A is a schematic side sectional view of a semiconductor processingdevice 1 comprising a reactor assembly 18, shown during a processingstage of the device 1. FIG. 1B is a schematic side sectional view of thesemiconductor processing device 1 of FIG. 1A, shown during a loadingstage of the device 1. The embodiment shown in FIGS. 1A-1B illustratesan ALD device, but it should be appreciated that the embodimentsdisclosed herein can be utilized in conjunction with any suitable typeof semiconductor processing device (e.g., any suitable type ofdeposition device). Furthermore, the semiconductor processing devices,control systems, and methods may be used in conjunction with theprocessing systems described throughout U.S. Pat. Nos. 8,211,230;8,216,380; U.S. patent application Ser. No. 15/803,615, filed Nov. 3,2017; U.S. patent application Ser. No. 15/785,231, filed Oct. 16, 2017;and U.S. Pat. No. 9,574,268, the entire contents of each of which arehereby incorporated by reference in their entirety and for all purposes.

The reactor assembly 18 can comprise an upper reaction chamber 2disposed above a lower loading chamber 8. The reaction chamber 2 can besized to receive a substrate (e.g., a semiconductor wafer) forprocessing. To load the reactor assembly 18, as shown in FIG. 1B, asusceptor 5 supported by a movable arm 6 can be lowered such that thesusceptor 5 is disposed in the loading chamber 8. In embodiments, thesusceptor 5 can include an internal heating mechanism, such as aresistive heater. A substrate (such as a wafer), not shown, can bepositioned on the susceptor 5. The movable arm 6 can be raisedvertically to position the substrate (not shown) within the reactionchamber 2. For example, the movable arm 6 can be raised such that anupper surface of the susceptor 5 is exposed to the reaction chamber 2. Apartition 9 can separate the reaction chamber 2 and the loading chamber8. In embodiments, there may be some limited fluid communication betweenthe loading chamber 8 and the reaction chamber 2 in the process position(FIG. 1A), such as through the illustrated small gap or series ofopenings between the susceptor 5 and the partition 9. As shown in FIGS.1A and 1B, a lower chamber (LC) pressure transducer 16 can be providedin the loading chamber 8 to measure the pressure in the loading chamber8. In the illustrated embodiment, no pressure measurement device ispresent in the reaction chamber 2 in order to avoid undesirable effectsupon gas flow in the reaction chamber 2.

During a deposition process, such as an ALD process, influent gases gi(e.g., reactant and/or inactive gases) can alternately and repeatedly besupplied to the reactor assembly 18 by way of an inlet manifold 7. Forexample, during a pulse or dose state of an ALD process, a reactant gascan be supplied to the reactor assembly 18 by way of the inlet manifold7. The reactant gas can react with a target species on the substrate toform a monolayer of the desired reactant. During a purge state, aninactive gas can be supplied to the reactor assembly 18 by way of theinlet manifold 7, to purge excess reactant (and other) gases from thereaction chamber 2. The dosing and purging steps can be alternatelyrepeated to grow the film a layer at a time until the layer reaches theoverall desired thickness. The influent gases gi can be dispersed overthe substrate in FIG. 1A by way of a showerhead assembly comprising ashowerhead plate 3 and a showerhead plenum 4 disposed above theshowerhead plate 3. The showerhead plate 3 can comprise a plurality ofopenings (not shown) which can evenly and uniformly disperse theinfluent gases gi over the substrate. Although a showerhead assembly isshown in FIGS. 1A-1B, it should be appreciated that other types ofreactors can be used in conjunction with the disclosed embodiments, suchas horizontal flow reactors.

The reactant and/or inactive gases in the reaction chamber 2 can beremoved from the reactor assembly 18 by a vacuum source 10 (e.g., avacuum pump) along an exhaust line 17. The vacuum source 10 can beactivated to apply a negative pressure to the exhaust line 17 and to thereaction chamber 2 to draw exhaust gases g_(e) from reactor assembly 18.As shown in FIG. 1A, the gases can exit the reaction chamber 2 by way ofone or a plurality of exhaust port(s) 13 that provide fluidcommunication between the reaction chamber 2 and the exhaust line 17. Inthe illustrated embodiment, the exhaust port(s) 13 feed an exhaust ringthat communicates with the exhaust line 17. A valve 14 (e.g., a flowcontrol valve) can be adjustably opened and closed at a plurality of setpoints or positions to meter the flow of exhaust gases g_(e) along theexhaust line 17. The plurality of set points or positions can correspondto a plurality of corresponding flow conductances of the valve 14. Thevalve 14 shown in FIGS. 1A-1B comprises a throttle valve that can beopened at a plurality of positions to increase or decrease the flow ofexhaust gases g_(e) through the exhaust line 17. For example, the valve14 can be positioned to be between 0% and 100% open, with 0%representing fully closed and 100% representing fully open, and any of avariety of positions therebetween. In other embodiments, as explainedbelow in connection with FIGS. 6A-6B, the valve 14 can comprise a ballvalve configured to control the flow of exhaust gases g_(e) through theexhaust line 17. As shown in FIGS. 1A-1B, an exhaust line pressuretransducer 15 can be provided along the exhaust line 17 to measure thepressure of exhaust gases g_(e) along the exhaust line 17.

As explained herein, a control system 19 can be configured to controlthe operation of the semiconductor processing device 1. The controlsystem 19 can comprise a module controller 11 and a valve controller 12.Although not shown, the control system 19 can comprise additionalcontrollers for controlling the overall operation of the device 1. Themodule controller 11 can be configured to select (automatically ormanually) the processing control modes, processing types, recipes used,and other parameters for a particular process. The module controller 11can communicate with the valve controller 12, which is configured tocontrol the operation of the valve 14. For example, as explained below,the module controller 11 can send instructions to the valve controller12 regarding the stage or state of the process (e.g., dose or purge), acontrol mode operation of the device 1 (e.g., whether the device 1 is tobe operated in open or closed loop control mode), a control pressure setpoint (e.g., for closed loop control), and a plurality of valve positionset points (e.g., fixed control positions of the valve 14). Furthermore,as explained below and based on instructions from the module controller11, the valve controller 12 can send instructions to the valve 14 toplace the valve at one of a plurality of set points corresponding to aplurality of flow conductances of the valve 14. Such instructions may bebased, for example, on a look-up table with a plurality of flowconductances or conductance ranges and a corresponding plurality ofvalve positions. The module controller 11 and the valve controller 12can comprise any suitable processing electronics for controlling theoperation of the valve 14 and/or other components of the processingdevice 1. For example, the module controller 11 and/or the valvecontroller 12 can comprise associated non-transitory computer-readablememory device(s) and processor(s) configured to execute instructionsstored on the associated memory device(s). In various embodiments, forexample, the valve controller 12 can comprise a programmable logiccontroller (PLC). Any other suitable types of controllers or processingelectronics can be used.

It can be desirable for overall flow rates and corresponding conductancethrough the reaction chamber 2 and the exhaust line 17 to vary in amulti-stage process, such as an atomic layer deposition (ALD) process.For example, during a purging state, to maximize throughput and reducereactant/byproduct residence time, it can be desirable to use high flowrates (gas loads) in order to rapidly purge excess or waste gases fromthe reaction chamber 2. During a depositing stage, such as an ALD dosingstate, however, it can be desirable to utilize a longer reactantresidence time at lower flow rates (gas loads) in order to achievesaturation (or near-saturation) with minimal waste of reactants. ManyALD processes seek to maintain a relatively constant overall flow rateand/or uniform pressure in the reaction chamber 2 during dosing andpurging in order to avoid pressure fluctuations and attendantcontamination issues (e.g., spalling). Accordingly, many ALD recipes usea constant overall gas load or flow rate. However, the use of a constantgas load may sacrifice purge efficiency and/or the quality of the filmdeposition.

In some arrangements, the pressure within the reaction chamber 2 can becontrolled using a closed loop control mode. For example, in somearrangements, the exhaust line pressure transducer 15 can be used tomeasure the pressure of the exhaust gases g_(e) along the exhaust line17. The measured pressure along the exhaust line 17 can be fed back tothe control system 19. Various control algorithms (e.g., aproportional-integral-derivative, or PID, control algorithm) can be usedto adjust the set points of the valve 14 to control the pressuremeasured by the transducer 15. However, basing the closed loop feedbackcontrol on pressure measurements taken by the exhaust line pressuretransducer 15 along the exhaust line 17 may be inaccurate and may notaccurately reflect the pressure (or changes in pressure) of gases withinthe reaction chamber 2, resulting in inaccurate or sub-optimal controlof the pressure in the reaction chamber 2. Similarly, the pressure inthe loading chamber 8 may not accurately reflect the pressure in thereaction chamber 2, due to the different flow rates and limited fluidcommunication between the chambers during processing, and as noted abovepressure measurement devices in the reaction chamber can interfere withdesired flow dynamics by creating dead legs or turbulence.

For example, the exhaust ports 13 may act as a restriction on theoutflow of gases from the reaction chamber 2 to the exhaust line 17. Theconstriction of the exhaust ports 13 may result in pressure readings bythe exhaust line pressure transducer 15 that are different from (e.g.,lower than) the actual pressure within the reaction chamber 2. Inaddition, as shown in FIGS. 1A-1B, the exhaust line pressure transducer15 may be spaced away from the reaction chamber 2 by an intervening flowvolume, e.g., by way of the exhaust portions 13 (and any interveningexhaust plenum) and the volume of the exhaust line 17 upstream of thetransducer 15. This additional volume upstream of the transducer 15 inthe space between the transducer 15 and the reaction chamber 2 may slowthe response of the closed loop control methods. Furthermore, closedloop feedback control of the valve 14 in high-speed ALD processes maynot be suitable, because the gas loads may change every 200-500milliseconds. Some throttle valves may not be capable of switching atsuch high speeds, and/or such rapid switching may damage the valves.Moreover, placing a pressure transducer within the reaction chamber 2itself may not be desirable, since the presence of the pressuretransducer 15 in such a small space may interfere with the flow patternsover the wafer and may negatively affect film growth.

Accordingly, there remains a continuing need for improved methods ofcontrolling the pressure in the reaction chamber 2. Various embodimentsdisclosed herein utilize open loop control (e.g., fixed position controlof the valve 14) to indirectly control the pressure within the reactionchamber 2 during dosing states and purging states. For example, in someembodiments, the LC transducer 16 can be used to measure the pressure inthe loading chamber 8 at various gas loads (flow rates) applied by thevacuum pump 10, and the measured pressure in the loading chamber 8 canbe correlated with corresponding set points or set positions of thevalve (representative of corresponding fluid conductances of the valve).In various embodiments, a flow controller (e.g., a pressure controlleror a master flow controller, or MFC) can be provided upstream of thereaction chamber 2 to adjust and/or provide the desired gas load. Asexplained herein, the valve 14 can act as a restriction on the flowthrough the exhaust line 17, which can change the pressure in thechamber 2 (see, e.g., FIG. 3 ). In the embodiments disclosed herein, thevacuum pump 10 can be activated at a constant speed, unless otherwisenoted. In other embodiments, however, the speed of the vacuum pump 10can vary during a procedure.

During a processing stage in which a substrate is undergoing adeposition process (FIG. 1A), the LC transducer 16 disposed in theloading chamber 8 may not accurately represent the pressure within theupper reaction chamber 2. For example, the reaction chamber 2 andloading chambers 8 may be isolated during processing so as to preventgases from flowing from the reaction chamber 2 into the loading chamber8. As shown in FIG. 1A, the partition 9 and the susceptor 5 may bespaced close together laterally by a small gap or by multiple openingsin the space between the partition 9 and the susceptor 5. In somearrangements, the pressure in the loading chamber 8 may be set at ahigher pressure than the reaction chamber 2, which in combination withthe close spacing of the partition 9 and susceptor 5, may prevent gasesfrom flowing into the loading chamber 8. Preventing gases from enteringthe loading chamber 8 can be beneficial in reducing contamination of theloading chamber 8 and the LC transducer 16 during transfer of wafers toand/or from the loading chamber 8, although other arrangements forminimizing contamination are also compatible with the embodiments taughtherein.

To calibrate the device 1 for open loop control, the movable arm 6 andsusceptor 5 may be moved vertically downward such that the susceptor 5is in the loading chamber 5, which breaks the fluid seal between thereaction and loading chambers 2, 8, such that the reaction and loadingchambers 2, 8 define a continuous volume or chamber. Therefore, when thesusceptor 5 is in the position shown in FIG. 1B, the LC transducer 16can represent the pressure in the reaction chamber 2, which in theposition shown in FIG. 1B, is in open and fluid communication with theloading chamber 8. The pressure in the reaction chamber 2 can bemeasured by the LC transducer 16 for a plurality of set points orpositions of the valve 14, across a plurality of gas loads (flow rates).The measured reaction chamber pressures, valve set points, and gas loadscan be stored in a look up table (LUT) and/or plotted in a graph toprovide input data to the control system 19. In other embodiments,pressures in the reaction chamber can be directly measured with thesusceptor in the process position for purposes of calibration, such aswith temporary or permanent instrumentation for direct pressuremeasurements in the reaction chamber.

FIG. 2 is a table of representative values of gas load (flow rate),valve control pressure, valve set point or position, measured waferpressure (i.e., pressure in the reaction chamber 2), and the differencebetween measured wafer pressure and control pressure. The table shown inFIG. 2 is representative of values obtained for a closed loop controlsystem. As shown in FIG. 2 , when the valve 14 is set at a controlpressure of 1 Torr, the pressure in the reaction chamber 2 can vary byover 800 mTorr as gas loads are increased by at least a factor of 10.This variance in gas load can cause a large variation in the reactionchamber 2 during a closed loop control mode. As shown in FIG. 2 , thevalve set point is typically more open with higher gas loads (e.g., apurging load at higher flow rates) to match the wafer pressure under alow gas load (e.g., dosing load at lower flow rates). As shown in FIG. 2, it can be important to improve the control of the variation inpressures for changing gas loads.

FIG. 3 is an example of a graph that plots measured reaction chamberpressures versus the set points of the valve 14, across a plurality ofgas loads. The graph shown in FIG. 3 is schematic, but can be consideredrepresentative of data provided in a LUT. As explained above, the graphof FIG. 3 (and corresponding LUT) can be generated by measuring(directly or indirectly) the pressure in the reaction chamber 2 for aplurality of set points or positions of the valve 14 at a firstparticular gas load or flow rate F₁. The gas load or flow rate F₁ can beincreased to a second gas load or flow rate F₂, and the pressure in thereaction chamber 2 can be measured for the plurality of set points ofthe valve 14 at the second flow rate F₂. The calibration can continueuntil the pressures and valve positions for all desired flow rates F_(N)have been determined. Thus, the LUT can comprise a matrix includingcalibrated values for pressure vs. valve set point (related to valveflow conductance) vs. gas load applied to the device 1 (e.g., by acontroller (such as a MFC or pressure controller) provided upstream ofthe chamber). The overall gas load or flow rate F can represent thetotal flow rate into the reaction chamber 2. In other embodiments, ananalytical function or curve-fit can be determined to relate reactionchamber set pressure, valve settings (conductances of the valve 14), andgas load (flow rate) provided by the pump 5. As shown in FIG. 3 , for aparticular flow rate, the pressure in the chamber may decrease withincreasing flow conductance of the valve (e.g., as related to how openthe valve is).

Thus, during an ALD process, the control system 19 (or the user) canselect a desired set pressure P_(set) for the reaction chamber 2 forboth dose and purge states, given the gas loads provided by a recipe forthose dose and purge states. For example, if the first lower flow rateF₁ is to be used during the dosing state (per the process recipe, with acontroller controlling the flow rate F₁), the control system 19 (or theuser) can determine first conductance settings of the valve 14, forexample, a first set position V₁ (Position 1) of the valve 14 along thecurve for the first flow rate F₁ that yields a pressure in the reactionchamber 2 of approximately P_(set). The control system 19 can instructthe valve 14 to move to the first set position V₁ during dosing. Afterthe dosing is complete, the control system 19 can turn off the flow ofreactant gas. If the second higher flow rate F₂ is to be used during thepurging state (per the recipe, with the controller controlling the flowrate F₂), the control system 19 (or the user) can determine secondconductance settings for the valve, for example, a second set positionV₂ (Position 2) of the valve 14 along the curve for the second flow rateF₂ that yields a pressure in the reaction chamber 2 of approximatelyP_(set). The control system 19 can instruct the valve 14 to move to thesecond set position V₂ during purging. Although the example abovedescribes one valve (or conductance) setting per state (dose or puge),it should be appreciated that in various embodiments, multiple valve orconductance settings can be used per state (dose or purge).

The example described above and illustrated in FIG. 3 assumes a desireto maintain the pressure of the reaction chamber 2 at an approximatelyconstant pressure during both purging and dosing to minimize pressurefluctuations and attendant contamination issues. Of course, the openloop control described herein can also be employed with differentpressure set points at different stages of a process if desired.Further, although only one purge and one dose step are described in thisexample ALD process, it should be appreciated that a particular cycle ofa deposition process can comprise more than one dose step and/or morethan one purge step. For example, some deposition processes (e.g., ALDprocesses) can comprise a cycle with four phases including, e.g., twodifferent reactant vapors (which may utilize different valveconductances and durations) and two different purges (which may or maynot have the same valve conductances and durations). Furthermore, somedeposition processes (e.g., ALD processes) may comprise a cycle thatpulses three different reactant vapors with one, two, or three purgephases in each cycle. Other deposition processes (e.g., ALD processes)may comprise a cycle that pulses four different reactant vapors withone, two, three, or four purge phases in each cycle.

Beneficially, the LUT described herein and the graph shown in FIG. 3 canenable the use of open loop, or fixed position, control in which noactive feedback is provided to the control system 19 by the exhaust linepressure transducer 15 (or other sensors) before switching valvepositions. Thus, when the device 1 is placed in a purging state, thevalve 14 can be set to a valve position or set position based on thedesired pressure at the purging flow rate. Similarly, when the device 1is placed in a dosing state, the valve 14 can be set to a valve positionor set position based on the desired pressure at the purging flow rate.The open loop control methods described herein can be superior to closedloop control, since the valve set positions correspond more accuratelyto the pressure in the reaction chamber 2 at various flow rates, asopposed to pressure measurements taken in real time along the exhaustline 17 by the transducer 15. Furthermore, the techniques disclosedherein can obviate the need for a pressure transducer 15 exposed toexhaust gases g_(e), in favor of using the LC transducer 16 that isisolated from gases of the reaction chamber 2 that may damage thetransducer. Accordingly, the open loop control methods disclosed hereinmay improve the control of pressure in the reaction chamber 2 duringvapor phase processing, particularly for processes with differentdesired overall flow rates at different stages, and even moreparticularly for processes with rapid switches between phases. Invarious ALD processes for example, the dosing stage can last for aperiod of time between about 50 msec and 5 sec.

In addition, various embodiments disclosed herein address additionaldrawbacks of closed loop pressure control systems related to digitaloutput of control signals. The set point or position of the valve 14shown in FIGS. 1A-1B (e.g., a throttle valve) can be adjusted bycontrolling the position of a plate or other structural member of thevalve 14 to adjustably limit flow through the valve 14 and exhaust line17. However, many closed loop control systems utilize digital outputs,which can make it challenging to precisely set the position of the valve14 at the desired analog set point calculated by the closed loop controlsystem. For example, in a closed loop control system, the control systemmay calculate an analog set point for the valve 14 that does not closelycorrelate to a digital output of the control system.

FIG. 4 is a schematic system diagram of the control system 19 inelectrical communication with the valve 14. As explained above inconnection with FIGS. 1A-1B, the module controller 11 can be configuredto control the operation of the valve controller 12, which in turn canbe configured to control the operation of the valve 14. In FIG. 4 , themodule controller 11 can comprise output signal blocks 11 a-11 e, eachof which comprise digital or analog output values that are to betransmitted to the valve controller 12 by way of a first communicationschannel 20 a. The first communications channel 20 a can comprise anysuitable wired or wireless electrical or data connection between themodule controller 11 and the valve controller 12.

For example, in a first output signal block 11 a of the modulecontroller 11, for an ALD process, a digital output DO2 can be providedto instruct whether the semiconductor processing device 1 is to beplaced in a dosing process of supplying reactant gas to the chamber 2 orin a purging process of removing excess gases from the chamber 2. Forexample, if the module controller 11 determines that the device 1 is tobe placed in a dosing state, then the DO2 signal can be set to 0 toindicate a dosing state with a low flow conductance that corresponds toPosition 1 (e.g., V₁ of FIG. 3 ) of the valve 14. By contrast, if themodule controller 11 determines that the device 1 is to be placed in apurging state then the DO2 signal can be set to 1 to indicate a purgingstate with a high flow conductance that corresponds to Position 2 (e.g.,V₂ of FIG. 3 ) of the valve 14. It should be appreciated throughout thedescription of FIG. 4 , that the signals could instead be set to 0 forthe purge state and to 1 for the dose state. Thus, digital output DO2 ofblock 11 a can instruct the valve controller 12 whether the device 1 isto be placed in a dose state or purge state.

In a second output block 11 b of the module controller 11, the digitaloutput DO1 can comprise instructions regarding the mode of control ofthe process, e.g., whether the device 1 is to operate in closed loopfeedback control (DO1=0) in which a pressure set point control will beprovided, or to operate with open loop (fixed position) control (DO1=1),in which valve positions are changed without realtime feedback. Staticanalog variables AO1-AO3 may be defined by a recipe step beforeprocessing, e.g., AO1-AO3 may be set by the control system 19 ormanually by the user (e.g., by way of a user interface). In a thirdblock 11 c, analog output AO1 may represent the closed loop controlpressure set point, which represents the desired set point pressure ifclosed loop control is selected. In a fourth block 11 d, analog outputAO2 may represent Position 1 of the valve 14, for example, position Vshown in FIG. 3 . As explained above, Position 1 may represent a lowflow conductance state to be used during pulsing of the reactant gas tothe reaction chamber 2. In a fifth block 11 e, analog output AO3 mayrepresent Position 2 of the valve 14, for example, position V₂ shown inFIG. 3 . As explained above, Position 2 may represent a high flowconductance state to be used during purging of excess gases in thereaction chamber 2. The digital and analog outputs from blocks 11 a-11 emay be transmitted to the valve controller 12 by way of the firstcommunications channel 20 a.

Turning to the valve controller 12, the instructions sent by the modulecontroller 11 may be received by analog or digital input blocks 12 a-12e. In a first block 12 a, digital input DI2 can correspond to digitaloutput DO2 from the module controller 11. Since the dosing and purgingsteps are alternated rapidly, the output and input blocks 11 a, 12 a canbe provided over a relatively high speed communications channel. Insecond through fifth input blocks 12 b-12 e, DI1 can represent thedigital mode selection sent from block 11 b of the module controller 11;AI1 can represent the analog pressure set control point sent from block11 c of the module controller 11; AI2 can represent Position 1 of thevalve 14 sent from block 11 d of the module controller 11; and AI3 canrepresent Position 2 of the valve 14 sent from block 11 e of the modulecontroller 11. Since the values in blocks 11 b-11 e and 12 b-12 e may beused for an entire process (or multiple processes), a slowercommunications network can be used.

The valve controller 12 can also include a plurality of logic blocks 12f, 12 g, and 12 h. Processing electronics can execute the instructionsstored on memory device(s) of the valve controller 12 to determine,inter alia, control mode of the device, process state (e.g., purge ordose), valve set position, pressure set point for closed loop control,etc. For example, in a first logic block 12 f, if DI1=0 (indicatingclosed loop control with pressure set point), then digital output DO1 ofthe valve controller 12 (see block 12 i) can likewise be set to 0 toindicate closed loop control, and analog output AO1 of the valvecontroller 12 (see block 12 j) can be set to the pressure control setpoint stored in AI1. In such an arrangement, the valve controller 12 cantransmit DO1 and AO1 to blocks 14 a, 14 b of the valve 14, respectively,over a second communications channel 20 b. With digital input DI=0 atthe valve 14, therefore, the valve 14 can operate in a closed loopfeedback mode. With analog input AI equal to the pressure set controlpoint at the valve 14, the device 14 can use the pressure set controlpoint to drive the closed loop feedback of the deposition process.

Alternatively, in a second logic block 12 g of the valve controller 12,if DI1=1 (indicating open loop control with a position set point) and ifDI2=0 (indicating that the valve should be located at Position 1), thendigital output DO1 of block 12 i is set to 1 and analog output AO1 ofblock 12 j is set to AI2 to represent Position 1 of the valve 14 (e.g.,V₁). Upon transmitting DO1 and AO1 of the valve controller 12 torespective blocks 14 a, 14 b of the valve 14 over the secondcommunications channel 20 b, digital input DI=1 at the valve 14, placingthe valve 14 in an open loop control mode (e.g., no feedback). Withanalog input A equal to Position 1, the valve 14 can move to Position 1(V₁) which is representative of a low flow conductance reactant pulsestate, as shown in FIG. 3 .

Similarly, in a third logic block 12 h of the valve controller 12, ifDI1=1 (indicating open loop control with a position set point) and ifDI2=1 (indicating that the valve should be located at Position 2), thendigital output DO1 of block 12 i is set to 1 and analog output AO1 ofblock 12 j is set to AI3 to represent Position 2 of the valve 14 (e.g.,V₂). Upon transmitting DO1 and AO1 of the valve controller 12 torespective blocks 14 a, 14 b of the valve 14 over the secondcommunications channel 20 b, digital input DI=1 at the valve 14, placingthe valve 14 in an open loop control mode (e.g., no feedback). Withanalog input AI equal to Position 2, the valve 14 can move to Position 2(V₂) which is representative of a high flow conductance purge state, asshown in FIG. 3 .

Beneficially, therefore, the embodiments disclosed herein can utilizedigital control systems to actuate a valve 14 having a continuous rangeof valve positions. The embodiments disclosed herein can select whetherto operate in closed loop control mode, or in an open loop control mode.

FIG. 5 is a flowchart illustrating a method 50 for operating an ALDdevice, according to various embodiments. In particular, the method 50illustrates various steps for controlling the pressure within thereaction chamber 2 using open loop control methods. Beginning in a block51, a first conductance setting of the valve corresponding to a firstflow conductance can be determined. For example, for the embodiment ofFIGS. 1A-1B and 3-4 , a first pre-programmed set point of the valve 14along the exhaust line 17 is determined. The first pre-programmed setpoint can be representative of a position of a movable member in thevalve 14 indicative of how open the valve 14 is (e.g., 0% to 100% open).The first pre-programmed set point can correspond to a first flowconductance setting of the valve 14 based at least in part on a firstdesired pressure in the reaction chamber 2 and on a first gas load to beapplied to the exhaust line 17. As explained above, a LUT (or graphrepresentative of a LUT) can be used to determine the firstpre-programmed set point or set position of the valve 14 based on adesired pressure and on the gas load (flow rate) being applied to thedevice, e.g., by way of a controller upstream of the reaction chamber 2.In other arrangements, an empirically designed function or curve-fit(e.g., based on curves similar to FIG. 3 ) can be used to relate thedesired pressure in the reaction chamber 2, the first flow conductancesetting of the valve 14, and the gas load. For example, the firstpre-programmed set point can correspond to a relatively low flowconductance to be used during the pulsing of reactant gas into thereaction chamber 2. Returning to the example shown in FIG. 3 , the firstpre-programmed set point of the valve can be determined to correspond toPosition 1 (or V). As explained above, the LUT can be created bymeasuring the pressure of the reaction chamber 2 and loading chamber 8using the LC transducer 16 when the susceptor 5 is disposed within theloading chamber 8 below the reaction chamber 2. Alternatively, pressuremay be directly measured in the reaction chamber 2 for calibration,e.g., using temporary or permanent instrumentation for this purpose.

Turning to a block 52, a second conductance setting of the valvecorresponding to a second flow conductance can be determined. Forexample, a second pre-programmed set point of the valve 14 along theexhaust line 17 can be determined. The second pre-programmed set pointcan correspond to the second flow conductance of the valve 14 based atleast in part on a second desired pressure in the reaction chamber 2 anda second gas load. In some embodiments, as explained above, the seconddesired pressure can be approximately the same as the first desiredpressure, so as to maintain a generally constant pressure in thereaction chamber 2 during dosing and purging steps. As explained above,the LUT (or graph representative of a LUT) can be used to determine thesecond pre-programmed set point or set position of the valve 14 based onthe second desired pressure and on the applied gas load (flow rate). Forexample, the second pre-programmed set point can correspond to arelatively high flow conductance to be used during the purging of excessor waste gas from the reaction chamber 2. Returning to the example shownin FIG. 3 , the second pre-programmed set point of the valve can bedetermined to correspond to Position 2 (or V₂).

In a block 53, the module controller 11 can instruct the valvecontroller 12 to place the valve 14 in the dosing state, e.g., at thefirst conductance setting. For dosing, the valve controller 12 caninstruct the valve 14 to move to Position 1 (V₁) to provide a relativelylow flow conductance during dosing. In a block 54, the control system 19can cause the semiconductor processing device 1 to pulse reactant gasinto the reaction chamber 2 to grow a layer of reactant on thesubstrate. After dosing, in a block 55, the module controller 11 caninstruct the valve controller 12 to place the valve 14 at the secondflow conductance state, e.g., at a valve setting for the purging state.For purging, the valve controller 12 can instruct the valve 14 to moveto Position 2 (V₂) to provide a relatively high flow conductance duringpurging. In a block 56, the control system 19 can cause thesemiconductor processing device 1 to purge excess or waste gas from thereaction chamber 2. Moving to a block 57, the control system 19 candetermine whether the process is to be repeated. If the determination isyes, then the method 50 returns to the block 53 to place the valve 14 atthe first flow conductance setting, e.g., the pre-programmed set point(Position 1) for pulsing additional reactant gas into the chamber 2. Ifthe determination is no, then the method 50 ends.

FIG. 6A is a schematic plan view of a valve 14 in a fully openconfiguration, according to various embodiments disclosed herein. FIG.6B is a schematic plan view of the valve 14 of FIG. 6A in a fully closedconfiguration. In some embodiments, the valve 14 shown in FIGS. 6A-6Bmay be used in connection with the semiconductor processing device 1described above in connection with FIGS. 1A-5 . In other embodiments,the semiconductor processing device 1 of FIGS. 1A-5 may utilize adifferent type of valve, such as the throttle valve described above.Further, it should be appreciated that the valve 14 of FIGS. 6A-6B maybe used in any suitable type of semiconductor processing system,including devices that are different from the semiconductor processingdevice 1 described above. Indeed, the valve 14 of FIGS. 6A-6B may beused in ALD devices, CVD devices, other types of deposition devices,non-deposition equipment (for example, etching equipment), or any othersuitable device that utilizes variable flow conductance through aconduit or pipe.

As explained above, it can be desirable to have variable flowconductance systems for semiconductor processing devices. For example,as explained above, it can be desirable to have a high flow conductance(high flow rate) during purging of the reaction chamber in order toimprove throughput and to remove excess gases before the subsequentdosing step. Further, it can be desirable to have a low flow conductance(low flow rate) during dosing so as to increase reactant gas residencetime in the reaction chamber. Moreover, recent semiconductor devicesutilize numerous layers (e.g., greater than 100 layers) that may havevarious surface topologies. For fabricating devices with a very largenumber of layers and complex surface topology, it can be important tofurther increase reactant gas residence times in the reaction chamber inorder to ensure that the larger surface area is covered by the reactantlayer, and at the same time it can be important to have low residencetimes in other phases of the process such as ALD purging. Other vaporprocessing may similarly call for different overall flow rates atdifferent stages of the process. Accordingly, there remains a continuingdemand for improved variable conductance devices for semiconductorprocessing.

The valve 14 can comprise a valve particularly suited for variableconductor processing and/or processing in a deposition reactor where thevalve is subject to adverse reactions (such as layer build-up that canclose the valve) by exposure to the reaction gases, particularly in theexhaust lines of a reactor. In the illustrated embodiment, the valve 14comprises a ball valve having a rounded valve body 31 with a bore 32provided through the valve body 31. In the illustrated embodiment, therounded valve body 31 comprises a ball-shaped (e.g., approximatelyspherical) member. A flange 35 can be provided on or around the exhaustline 17. The valve body 31 can be seated within the flange 35 with a gapprovided between the valve body 31 and an inner surface of the flange 35so as to allow rotation of the valve body 31 relative to the flange 35.A motor 30 can be operably coupled with the valve body 31 by way of amotor output shaft 36. For example, the output shaft 36 can be welded orotherwise mechanically connected to the valve body 31. When activated,the motor 30 can impart rotation to the output shaft 36 and, in turn, tothe valve body 31 to cause the valve body 31 to rotate R about alongitudinal or rotational axis x parallel to the output shaft 36. Themotor 30 can operate at high speeds (e.g., at least about 1000 rpm) toyield fast purge-dose-purge-dose cycles (e.g., one cycle in 60 ms).

As shown in FIGS. 6A-6B, the bore 32 formed through the valve body 31can be oriented non-parallel to (e.g., perpendicular to) the rotationalor longitudinal axis x of the motor 30. In FIG. 6A, the motor 30 canposition the bore 32 such that the bore 32 is parallel to a flow axis yof the exhaust line 17. When the bore 32 is parallel to the flow axis yof the exhaust line 17, the valve 14 can be considered to be in amaximum flow conductance state, in which the valve 14 is fully open topermit gases to flow through the exhaust line 17. By contrast, in FIG.6B, the motor 30 can position the bore 32 such that the bore 32 isoriented perpendicular to the flow axis y of the exhaust line 17. In thearrangement of FIG. 6B, the perpendicularly-oriented bore 32 can blocksubstantially all gases from flowing through the valve 14 and theexhaust line 17. Thus, when the bore 32 is oriented perpendicular to theflow axis y of the exhaust line 17, the valve 14 can be considered to bein a minimum flow conductance state, in which the valve 14 substantiallyblocks gases from flowing through the exhaust line 17. As will be clearfrom the description below, the valve 14 is not limited to these twostates but instead can rotate, at variable rotational speeds, through aninfinite number of degrees of opening.

As shown in FIGS. 6A-6B, the valve 14 can further comprise an inactivegas curtain region 33 disposed about the periphery of the valve body 31.The inactive gas curtain region 33 can comprise a region of inactive gasthat is supplied through an inlet port into the gap between the flange35 and the outer periphery of the valve body 31. The inactive gascurtain 33 can comprise an externally purged area around the valve body31 that creates ballast around the valve body 31. When the valve 14 isin the open configuration shown in FIG. 6A, the inactive gas curtainregion 33 can beneficially prevent reactant or other gases from enteringthe gap on the outer periphery of the valve body 31, which can reducethe risk of contamination and maintain the fast performance of the valve14. The inactive gas curtain 33 can allow low friction rotation aboutthe rotational axis x.

FIGS. 6A-6B illustrate two states of the valve (maximum and minimum flowconductances, respectively), but beneficially, the valve 14 can beplaced in a plurality of orientations about the rotational axis x. Invarious embodiments, the valve body 31 and bore 32 can be placed in acontinuous range of orientations or angles about the rotational axis x,e.g., in a range of 0° to 360°. The valve body 31 and bore 32 can berotated in both directions about the rotational axis x. The valve body31 and bore 32 can be placed in numerous orientations in which the bore32 is exposed to the gas along the exhaust gas line 17. If the bore 32is angled relative to the gas line 17 such that only a small area of thebore 32 is exposed to the exhaust gas line 17, then the flow ratethrough the valve 14 will be relatively low. If the bore 32 is angledrelative to the gas line 17 such that a relatively large area of thebore 32 is exposed to the exhaust gas line, then the flow rate throughthe valve 14 will be higher. The motor 30 can precisely control theorientation of the valve body 31 and bore 32 about the rotational axisx, and this orientation can be correlated with flow rates through thebore 32. Beneficially, therefore, the ability to orient the bore 32 at aplurality of angles relative to the rotational axis x, the valve 14shown in FIGS. 6A-6B can provide for variable flow conductances throughthe exhaust gas line 17. In some embodiments, the valve 14 can providefor a continuous of angles about the rotational axis x, and accordinglya continuous range of flow rates through the valve 14 and gas line 17.

To control the orientation of the valve body 31 and bore 32, anorientation sensor 34 can be provided on the flange 35 near the valvebody 31. The orientation sensor 34 can remain stationary as the valvebody 31 rotates. The orientation sensor 34 can measure the orientationby sensing the leading edge 37 of the bore 32, the trailing edge 38 ofthe bore, and regions of the bore 32 between the leading and trailingedges 37, 38. In various embodiments, the orientation sensor 34 cancomprise a magnetic sensor, but other types of sensors may be used. Invarious embodiments, for example, a motor encoder can be used to sensethe orientation of the valve body 31. The control system 19 can also beused to control the orientation of the valve body 31 and bore 32. Forexample, the control system 19 can comprise processing electronicsconfigured to control the operation of the motor 30 and/or to receivesignals transduced by the orientation sensor 34. In some embodiments,the control system 19 can utilize feedback control techniques, in whichan orientation set point for the valve 14 is provided, which cancorrespond to a desired flow conductance. The control system 19 canreceive a signal from the orientation sensor 34 representative of thecurrent orientation of the valve body 31 and bore 32. Based on thedifference between the orientation set point and the currentorientation, the control system can utilize various control techniques(including, e.g., PID control techniques) to send an instruction signalto the motor 30 to cause the motor 30 to rotate the valve body 31 to thedesired orientation set point corresponding to the desired flowconductance.

During a purge cycle or state, the control system 19 can instruct themotor 30 to rotate the valve body 31 and bore 32 at one or a pluralityof orientations corresponding to a desired or pre-programmed relativelyhigh flow conductance. Thus, during a particular phase (dosing orpurging), the average conductance can be changed by controlling thespeed of rotation. For example, the rotational speed of the valve body31 and bore 32 can be slowed during dosing to reduce the averageconductance, and/or increased during purging to increase the averageconductance. In some embodiments, the motor 30 can continuously rotatethe valve body 31 and bore 32 during purge and dose states. For example,the motor 30 can rotate the valve body 31 and bore 32 at highervelocities during purging, and/or can expose a larger area of the bore32 to the exhaust line 17 during purging. In some embodiments, the motor30 can rotate the valve body 31 and bore 32 at lower velocities duringdosing, and/or can expose a smaller area of the bore 32 to the exhaustline 17 during dosing. In some embodiments, the motor 30 can stop therotation of the valve body 31 and bore at a particular orientationduring purging and/or dosing. For example, during purging, the motor 30may stop rotating the valve body 31 and bore 32 at an orientation thatmaximizes or increases flow conductance (e.g., as shown in FIG. 6A). Asanother example, during dosing, the motor 30 may stop rotating the valvebody 31 and bore 32 at an orientation that minimizes or reduces flowconductance so as to increase reactant vapor residence time in thereaction chamber 2. As explained above, the control system 19 canutilize feedback control techniques based on the signals from theorientation sensor 34.

FIG. 7 is a graph of relative flow conductance over time for a purgecycle, followed by a dose cycle, followed by another purge cycle, usingthe valve 14 shown in FIGS. 6A-6B. As shown for the purge pulse, thecontrol system 19 can instruct the motor 30 to place the valve 14 at oneor a plurality of conductance settings that increases or maximizes flowconductance, e.g., the orientation shown in FIG. 6A in which the bore 32is generally parallel to the flow axis y of the exhaust gas line 17.Providing high flow conductance setting(s) during purge results in thehigh flow rates during the purging cycles. As explained herein, thecontrol system 19 and motor 30 can control the angular velocity andacceleration of the valve body 31 and bore 32 about the rotational axisx during a particular processing phase (dose or puge) and/or betweenprocessing phases. During purging, the motor 30 can rotate the valvebody 31 at a high velocity in order to terminate the purge cycle beforethe next dosing cycle.

During dosing, by contrast, the valve 14 can be set at one or morerelatively low flow conductance setting(s), resulting in relatively lowflow rates as shown in FIG. 7 . For example, the bore 32 can be moved ina manner that reduces the flow through the valve 14. For example, insome embodiments, the velocity of rotation of the valve 14 can be slowedand/or the area of the bore 32 exposed to the exhaust line 17 can bemade relatively small, e.g., at a relatively large angle (but less than90°) relative to the flow axis y at various orientations of the valvebody 31 during dosing. The relatively large angles and/or low angularvelocities can expose a small portion of the bore 32 to the exhaust line17 for a longer period of time, resulting in low flow rates and longerresidence times during dosing. Furthermore, during dosing, the angularvelocity of the valve body 31 and bore 32 can be relatively low so as tocause the reactant gas in the reaction chamber 2 to become relativelystagnant, causing an increased residence time in the chamber 2 andimproved formation of the layers.

Accordingly, the ball valve 14 shown in FIGS. 6A-7 can beneficiallyprovide high-speed, variable flow conductance for any suitable type ofsemiconductor processing device. In some embodiments, the valve 14 ofFIGS. 6A-7 can be placed along the exhaust line 17 of a semiconductorvapor phase processing device. In some embodiments, the device is avapor deposition device. In some embodiments, the device is a cyclicalCVD device. In some embodiments, the device is an ALD device. Further,the inactive gas curtain 33 can beneficially block reactant gases fromcontaminating the outer periphery of the valve body 31 when the bore 32is at least partially exposed to the exhaust line 17.

Although the foregoing has been described in detail by way ofillustrations and examples for purposes of clarity and understanding, itis apparent to those skilled in the art that certain changes andmodifications may be practiced. Therefore, the description and examplesshould not be construed as limiting the scope of the invention to thespecific embodiments and examples described herein, but rather to alsocover all modification and alternatives coming with the true scope andspirit of the invention. Moreover, not all of the features, aspects andadvantages described herein above are necessarily required to practicethe present invention.

What is claimed is:
 1. A method of controlling an atomic layerdeposition (ALD) device comprising a reaction chamber, an exhaust lineconnected to the reaction chamber that transfers gas out of the reactionchamber, a valve along the exhaust line, a susceptor configured tosupport a substrate, a loading chamber below the reaction chamber, apartition separating the loading chamber from the reaction chamber, aninlet manifold connected to the reaction chamber, and a lower chamberpressure transducer exposed to the loading chamber, the methodcomprising: controlling a dose state and a purge state of the ALD deviceaccording to an open loop control scheme, comprising: forming a storedlook-up table (LUT), comprising: positioning the susceptor in theloading chamber such that the loading chamber is in fluid communicationwith the reaction chamber, and for the plurality of preset gas loadsalong the exhaust line, measuring pressures in the loading chamber for aplurality of set points of the valve; accessing the stored look up table(LUT), the LUT comprising a plurality of predetermined flow conductancesettings of the valve corresponding to a non-zero flow conductance, aplurality of associated preset gas loads and a plurality of associatedpressure values; for the dose state of the ALD device, selecting apredetermined first non-zero flow conductance setting from the pluralityof predetermined flow conductance settings of the valve corresponding toa first non-zero flow conductance based at least in part on a firstdesired pressure in the reaction chamber and a preset first gas load,from the plurality of preset gas loads, and sending a first signal tothe valve corresponding to the selected first non-zero flow conductancesetting, for the dose state; for a purge state of the ALD device,selecting a predetermined second non-zero flow conductance setting fromthe plurality of predetermined flow conductance settings of the valvecorresponding to a second non-zero flow conductance based at least inpart on a second desired pressure in the reaction chamber and a presetsecond gas load, from the plurality of preset gas loads, and sending asecond signal to the valve corresponding to the selected second non-zeroflow conductance setting, wherein the first signal is different from thesecond signal, for the purge state; placing the valve at the selectedfirst non-zero flow conductance setting for at least a portion of thedose state; pulsing a first reactant vapor into the reaction chamberduring the dose state; placing the valve at the selected second non-zeroflow conductance setting for at least a portion of the purge state; andpurging the reaction chamber by supplying an inactive gas to thereaction chamber during the purge state.
 2. The method of claim 1,wherein the first desired pressure is approximately the same as thesecond desired pressure.
 3. The method of claim 1, further comprisingplacing the valve at a plurality of first non-zero flow conductancesettings during the dose state, and placing the valve at a plurality ofsecond non-zero flow conductance settings during the purge state.
 4. Themethod of claim 1, wherein the flow conductance settings correspond toan open percentage of the valve.
 5. The method of claim 1, supplying aninactive gas to the reaction chamber during the purge state comprisessupplying an inactive gas to the reaction chamber at the preset secondgas load.
 6. The method of claim 1, pulsing a first reactant vapor intothe reaction chamber during the dose state comprises pulsing the firstreactant vapor at the preset first gas load into the reaction chamber.